Wide angle automatic exposure control in tomosynthesis

Abstract

The present application discloses a system and method to calculate the automatic exposure control (AEC) calibrated dosage for tomosynthesis sweeps. For example, reference images may be acquired, and corresponding reference detector count maps may be generated and stored for a plurality of projection angles using the tomosynthesis imaging system. The tomosynthesis imaging system may then acquire a scout image using a scout dosage, identify the densest region within the scout image, and calculated the average detector count values associated with the densest region. The AEC calibrated dosage can be calculated based on a ratio of the average reference detector count values, corresponding to the detector count values of pixels with a corresponding densest region of the reference image, and the calculated average detector count values.

The invention claimed is: 
     
         1 . A tomosynthesis system for performing an automatic exposure control (AEC) operation, the system comprising:
 a processor;   memory including instructions that when executed by the processor cause the processor to:
 acquire a scout image of a patient's breast at a first projection angle relative to a 0 degree normal direction to the patient's breast by emitting a scout x-ray dosage towards the patient's breast with the tomosynthesis system, the scout image including a plurality of pixels, wherein each of the plurality of pixels is associated with a detector count value from among a plurality of detector count values; 
 identify a first region on the scout image as corresponding to a densest portion of the patient's breast; 
 calculate an average detector count value by averaging the one or more detector count values corresponding to the one or more pixels within the first region; 
 identify a second region on a first reference image associated with the first projection angle, wherein the second region corresponds to a location on the first reference image that matches a location of the first region on the scout image; 
 obtain one or more reference detector count values associated with one or more reference pixels within the second region of the first reference image; 
 calculate an average reference detector count value by averaging the one or more reference detector count values; 
 based on a ratio between the average reference detector count value and the average detector count value, calculate an AEC calibrated dosage to use in a tomosynthesis scan; and 
 set a radiation dosage for a tomosynthesis sweep at a plurality of projection angles on the patient's breast to the AEC calibrated dosage. 
   
     
     
         2 . The tomosynthesis system of  claim 1 , wherein obtaining the one or more reference detector count values includes:
 extracting the one or more reference detector count values from a reference detector count map associated with the first projection angle,   wherein the reference detector count map associated with the first projection angle is one of a plurality of reference detector count maps that are generated in a calibration process prior to acquiring the scout image.   
     
     
         3 . The tomosynthesis system of  claim 2 , wherein the calibration includes:
 acquiring a plurality of reference images of a phantom, wherein each of the plurality of reference images is acquired using the tomosynthesis system at each of the plurality of projection angles and each of the plurality of reference images include a plurality of reference image pixels;   determining detector count values corresponding to each of the plurality of reference image pixels within each of the plurality of reference images; and   generating the plurality of reference detector count maps corresponding to each of the plurality of projection angles by compiling the plurality of reference image pixels and corresponding detector count values associated with each of the plurality of projection angles.   
     
     
         4 . The tomosynthesis system of  claim 2 , wherein when the first projection angle is not one of the plurality of projection angles that includes the reference detector count map, obtaining the reference detector count values associated with the one or more reference pixels from the second region of the first reference image includes:
 estimating the reference detector count values by performing (i) an interpolation function, (ii) an extrapolation function (iii) or a polynomial curve fitting function.   
     
     
         5 . The tomosynthesis system of  claim 1 , wherein the plurality of projection angles includes a range of angles that is between about −60 degrees and about +60 degrees relative to the patient's breast. 
     
     
         6 . The tomosynthesis system of  claim 1 , wherein calculating the AEC calculated dosage includes multiplying the scout x-ray dosage with the ratio between the average reference detector count value and the average detector count value, and a global scaling factor. 
     
     
         7 . The tomosynthesis system of  claim 1 , wherein the scout x-ray dosage includes a combination of: voltage used to generate a radiation from an x-ray source (kV), x-ray cathode to anode tube current (mA) and a length of time(s) to expose the patient to the radiation. 
     
     
         8 . The tomosynthesis system of  claim 1 , wherein the scout x-ray dosage is less than 10% of the AEC calculated dosage. 
     
     
         9 . The tomosynthesis system of  claim 1 , wherein identifying the densest portion of the patient's breast includes:
 applying a gain map associated with the first projection angle to the scout image to compensate for angle effects; and   identifying pixels within pre-identified center region that includes the lowest detector count values.   
     
     
         10 . A method of performing an automatic exposure control (AEC) operation using a tomosynthesis system, the method comprising:
 acquiring a scout image of a patient's breast at a first projection angle by emitting a scout x-ray dosage towards the patient's breast with the tomosynthesis system, the scout image including a plurality of pixels, wherein each of the plurality of pixels is associated with a detector count value from among a plurality of detector count values;   identifying a first region on the scout image as corresponding to a densest portion of the patient's breast;   calculating an average detector count value by averaging the one or more detector count values corresponding to the one or more pixels within the first region;   identifying a second region on a first reference image associated with the first projection angle, wherein the second region corresponds to a location on the first reference image that matches a location of the first region on the scout image;   obtaining one or more reference detector count values associated with one or more reference pixels within the second region of the first reference image;   calculating an average reference detector count value by averaging the one or more reference detector count values;   based on a ratio between the average reference detector count value and the average detector count value, calculating an AEC calibrated dosage to use in a tomosynthesis scan; and   setting a radiation dosage for a tomosynthesis sweep at a plurality of projection angles on the patient's breast to the AEC calibrated dosage.   
     
     
         11 . The method of  claim 10 , wherein obtaining the one or more reference detector count values includes:
 extracting the one or more reference detector count values from a reference detector count map associated with the first projection angle,
 wherein the reference detector count map associated with the first projection angle is one of a plurality of reference detector count maps that are generated in a calibration process prior to acquiring the scout image. 
   
     
     
         12 . The method of  claim 11 , wherein the calibration process includes:
 acquiring a plurality of reference images of a phantom, wherein each of the plurality of reference images is acquired using the tomosynthesis system at each of the plurality of projection angles and each of the plurality of reference images include a plurality of reference image pixels;   determining reference image detector count values corresponding to each of the plurality of reference image pixels within each of the plurality of reference images; and   generating the plurality of reference image detector count maps corresponding to each of the plurality of projection angles by compiling the plurality of reference image pixels and corresponding reference image detector count values associated with each of the plurality of projection angles.   
     
     
         13 . The method of  claim 11 , wherein when the first projection angle is not one of the plurality of projection angles that includes the reference detector count map, obtaining the reference detector count values associated with the one or more reference pixels from the second region of the first reference image includes:
 estimating the reference detector count values by performing (i) an interpolation function, (ii) an extrapolation function or (iii) a polynomial curve fitting function.   
     
     
         14 . The method of  claim 10 , wherein the plurality of projection angles includes a range of angles that is between about-60 degrees and about +60 degrees relative to the patient's breast. 
     
     
         15 . The method of  claim 10 , wherein calculating the AEC calculated dosage includes multiplying the scout x-ray dosage with the ratio between the average reference detector count value and the average detector count value, and a global scaling factor. 
     
     
         16 . The method of  claim 10 , wherein the first projection angle is based on a current position of the tomosynthesis system prior to acquiring the scout image. 
     
     
         17 . The method of  claim 16 , wherein the current position is different than 0 degree angle relative to the patient's breast. 
     
     
         18 . The method of  claim 10 , further comprising:
 acquiring the scout image of the patient's breast at a second projection angle that is different than the first projection angle.   
     
     
         19 . The method of  claim 10 , wherein identifying the densest portion of the patient's breast includes:
 applying a gain map associated with the first projection angle to the scout image to compensate for angle effects; and   identifying pixels within pre-identified center region that includes the lowest detector count values.   
     
     
         20 . A method of performing a calibration operation associated with an automatic exposure control (AEC) operation using a tomosynthesis system, the method comprising:
 acquiring a plurality of reference images of a phantom at a plurality of projection angles, wherein each of the plurality of reference images include a plurality of reference image pixels;   generating a plurality of reference image detector count maps corresponding to each of the plurality of reference images by compiling a plurality of reference image pixels and corresponding reference image detector count values associated for each of the plurality of reference images;   storing the plurality of reference image detector count maps;   acquiring a scout image of a patient's breast at the first projection angle by emitting a scout x-ray dosage towards the patient's breast with the tomosynthesis system, the scout image including a plurality of pixels, wherein each of the plurality of pixels is associated with a detector count value from among a plurality of detector count values;   identifying a first region on the scout image as corresponding to a densest portion of the patient's breast;   calculating an average detector count value by averaging the one or more detector count values corresponding to the one or more pixels within the first region;   identifying a second region on a first reference image associated with a first projection angle, wherein the second region corresponds to a location on the first reference image that matches a location of the first region on the scout image and the first projection angle is one of the plurality of projection angles and the first reference image is one of the plurality of reference images;   obtaining one or more reference detector count values associated with one or more reference pixels within the second region of the first reference image;   calculating an average reference detector count value by averaging the one or more reference detector count values;   based on a ratio between the average reference detector count value and the average detector count value, calculating an AEC calibrated dosage to use in a tomosynthesis scan; and   setting a radiation dosage for a tomosynthesis sweep at a plurality of projection angles on the patient's breast to the AEC calibrated dosage.